Conventional tufting machines for forming tufted articles such as carpets typically include one or two needle bars having a series of spaced needles that extend across the width of the tufting machine and which insert a series of yarns into a backing material that is being passed through a tufting zone of the tufting machine. Typically, the backing material used will be a woven or knitted synthetic fabric material that is fed from a supply roll over front and rear backing feed rolls into and through the tufting zone of the tufting machine. Due to the inherent ability of most backing materials to stretch, there is a tendency of the backing material to “neck in,” which is where the side edges of the backing material are drawn inwardly as the backing material is pulled through the tufting zone, causing it to be stretched longitudinally. This necking in of the backing material can cause side matching problems in finished carpets, especially patterned carpets, such that the patterned elements formed along the side edges of carpets cannot be properly matched together. In addition, in staggered needle tufting machines, due to necking in of the backing material, the gauge of the needle tuft rows becomes narrowed, leading to differences in texture and color of the carpets also can be created along the sides of the carpets.
Accordingly, attempts have been made to try to pre-stretch the primary backing material as it is fed into the tufting zone of the tufting machine such as through the use of tenter frames and magnetic clutches or brakes added to the spike rolls of the tufting machine. Other attempts to solve these tensioning problems have further included the use of load cells on the rear backing feed roll for the tufting machine, which roll generally has been gear driven off the main shaft of the tufting machine or electronically ratioed with a servomotor, with adjustments being based upon the operation of the main shaft of the tufting machine. However, a problem still exists with respect to maintaining tension on the backing material as it is fed through the tufting machine, especially as the amount, and thus the weight, of backing material remaining on the supply roll decreases, which can accordingly decrease the drag or tension applied to the backing material by the weight of the supply roll itself and vary the load on the front spike roll.
Accordingly, it can be seen that a need exists for a system and method of controlling tension in a backing material being fed to a tufting machine that addresses the foregoing and other related and unrelated problems in the art.